Cardiac enzyme studies measure the levels of the
enzyme creatine phosphokinase (CPK, CK) and the
protein troponin (TnI, TnT) in the blood. Low levels
of these enzymes and proteins are normally found in your blood, but if your
heart muscle is injured, such as from a
heart attack, the enzymes and proteins leak out of
damaged heart muscle cells, and their levels in the bloodstream rise.
Because some of these enzymes and proteins are also found in other
body tissues, their levels in the blood may rise when those other tissues are
damaged. Cardiac enzyme studies must always be compared with your symptoms,
your physical examination findings, and
electrocardiogram (EKG, ECG) results.
Why It Is Done
Cardiac enzyme studies are done to:
Determine whether you are having a heart attack
or a threatened heart attack (unstable angina) if you have chest
pain, shortness of breath, nausea, sweating, and abnormal electrocardiography
results.
Determine if a procedure,
such as percutaneous coronary intervention (PCI), or a medicine to dissolve the
blockage (thrombolytic medicine) has successfully restored blood flow through a
blocked coronary artery.
How To Prepare
No special preparation is required before having this test.
Many medicines may affect the results of this test. Be sure to tell
your health professional about all the nonprescription and prescription
medicines you take.
Talk to your doctor about any concerns you have regarding the need
for the test, its risks, how it will be done, or what the results will
indicate. To help you understand the importance of this test, fill out the
medical test information form(What is a PDF document?)
.
How It Is Done
The health professional drawing your blood will:
Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.
Clean the needle site with
alcohol.
Put the needle into the vein. More than one needle stick
may be needed.
Attach a tube to the needle to fill it with
blood.
Remove the band from your arm when enough blood is
collected.
Put a gauze pad or cotton ball over the needle site as
the needle is removed.
Put pressure on the site and then put on a
bandage.
Cardiac enzyme studies are often repeated over several hours for
comparison. Blood samples for these cardiac enzyme tests are usually drawn
every 8 to 12 hours for 1 to 2 days after a suspected heart attack, to look for
the rise and fall in the enzyme levels.
How It Feels
The blood sample is taken from a vein in your arm. An elastic band
is wrapped around your upper arm. It may feel tight. You may feel nothing at
all from the needle, or you may feel a quick sting or pinch.
Risks
There is very little chance of a problem from having blood sample
taken from a vein.
You may get a small bruise at the site. You can
lower the chance of bruising by keeping pressure on the site for several
minutes.
In rare cases, the vein may become swollen after the
blood sample is taken. This problem is called phlebitis. A warm compress can be
used several times a day to treat this.
Ongoing bleeding can be a
problem for people with bleeding disorders. Aspirin, warfarin (Coumadin) and
other blood-thinning medicines can make bleeding more likely. If you have
bleeding or clotting problems, or if you take blood-thinning medicine, tell
your doctor before your blood sample is taken.
Results
Cardiac enzyme studies measure the levels of the
enzyme creatine phosphokinase (CPK, CK) and the
protein troponin (TnI, TnT) in the blood.
Test results are usually available within an hour.
Values and units for reporting the results of cardiac enzyme tests
vary considerably from lab to lab. The values listed below can be used as a
general guide. Check with your lab or doctor for specific values.
Elevated troponin may be present when you have heart muscle
injury. Blood levels of troponin typically rise within 4 to 6 hours after a
heart attack, reach their highest levels within 10 to 24 hours, and fall to
normal levels within 10 days.
CPK levels generally rise within 4 to 8 hours after a heart
attack, reach their highest levels within 12 to 24 hours, then return to normal
within 3 to 4 days.
CPK-MB is found in large amounts in the heart muscle. A
CPK-MB greater than 3.0 ng/mL may be present when you have muscle damage caused
by a heart attack. Blood levels of CPK-MB typically rise within 2 to 6 hours
after a heart attack, reach their highest levels within 12 to 24 hours, and
fall to normal levels within 3 days.
An ongoing high level of CPK-MB levels after 3 days may
mean that a heart attack is progressing and more heart muscle is being
damaged.
What Affects the Test
Reasons you may not be able to have the test or why the results may
not be helpful include:
Cardiac enzyme and protein levels must always
be compared with your symptoms, medical history, physical examination, and
electrocardiography (EKG, ECG) results.
Troponin is an accurate
method for quickly diagnosing heart attack, but because it takes up to 6 hours
for the troponin level to rise, it can be low or negative at first. Troponin is
more specific to heart muscle and remains in the bloodstream longer than
CPK.
CPK-MB, which is found in large amounts in damaged heart
muscle, is a more specific way to estimate the amount of heart muscle damage
than total CPK. The total CPK enzyme level can be elevated from vigorous
exercise, intramuscular injections, crush injuries to muscles, muscular
dystrophy, or muscle inflammation.
Another protein,
myoglobin, may be tested along with cardiac enzymes to
diagnose a heart attack.
This information does not replace the advice of a doctor. Healthwise disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.
